Sealing material for annular barriers

ABSTRACT

The present invention relates to an annular barrier for providing zone isolation between a first zone and a second zone in a borehole or a casing downhole, the annular barrier comprising a tubular part and an expandable element made of metal surrounding the tubular part, and the annular barrier having a circumference, a longitudinal extension and an outer face and further comprising an annular seal comprising a sealing material, the sealing material extending around the outer face of the annular barrier and having a bundle of strands wherein at least one strand comprises graphite and/or carbon.

FIELD OF THE INVENTION

The present invention relates to an annular barrier for providing zoneisolation between a first zone and a second zone in a borehole or acasing downhole. The invention furthermore relates to a downhole systemand a method.

BACKGROUND ART

Annular barriers or packers downhole often comprise an external sealingmaterial, such as elastomeric circumferential rings, to improve thesealing ability of the annular barrier when expanded to abut the innerwall of a casing or borehole.

When expanding annular barriers or packers, the sealing material isexpanded accordingly, thereby decreasing the sealing ability.Furthermore, the sealing ability of the elastomeric material isdecreased when subjected to the harsh environment downhole, such as hightemperatures and pressure and different kinds of acid.

Annular barriers may be part of a completion for many years withoutbeing expanded, while the elastomeric seals are continuously subjectedto the harsh environment and disintegrates and thus deteriorates overthat time. This means that when the annular barrier is eventuallyexpanded, the sealing ability of the elastomeric material may be lost.

SUMMARY OF THE INVENTION

It is an object of the present invention to wholly or partly overcomethe above disadvantages and drawbacks of the prior art. Morespecifically, it is an object to provide an improved annular seal forannular barriers capable of withstanding the harsh environment downhole,such as high temperatures, high pressure and acid, over a period of timeof approximately 10 to 20 years.

The above objects, together with numerous other objects, advantages, andfeatures, which will become evident from the below description, areaccomplished by a solution in accordance with the present invention byan annular barrier for providing zone isolation between a first zone anda second zone in a borehole or a casing downhole, the annular barriercomprising a tubular part and an expandable element made of metalsurrounding the tubular part, and the annular barrier having acircumference, an longitudinal extension and an outer face and furthercomprising an annular seal comprising a sealing material, the sealingmaterial extending around the outer face of the annular barrier andhaving a bundle of strands wherein at least one strand comprisesgraphite and/or carbon.

In one embodiment, the expandable element may be an expandable sleevesurrounding a tubular part and may be connected with the tubular part.

Furthermore, the expandable element may be one or more expandable tubesextending around the tubular part.

Moreover, the strands may comprise at least 30% graphite and/or carbon,preferably at least 50% graphite and/or carbon, more preferably at least75% graphite and/or carbon, and even more preferably at least 90%graphite and/or carbon.

In addition, each strand may comprise graphite and/or carbon.

In an embodiment, the sealing material may cover less than 60% of theouter face, preferably less than 40% of the outer face, more preferablyless than 30% of the outer face.

Also, the annular seal may extend around the outer face of the annularbarrier.

Moreover, a cross-sectional shape of the annular seal may substantiallybe a triangle, a square, a pentagon, a hexagon, or a shape having moresides.

Further, the sealing material may be wound around the outer face of theannular barrier with x windings, where x>1.0.

x may be between 1.0 and 2.0, preferably between 1.1 and 1.7 and morepreferably between 1.2 and 1.5.

Additionally, the annular seal may have an elongated shape and two ends.

In one embodiment, the ends may overlap when seen in the longitudinalextension.

Furthermore, the annular seal may be arranged side by side around theouter face as windings.

Moreover, the windings may be arranged side by side around the outerface without any material between the windings.

Furthermore, the annular barrier may comprise several annular seals.

Also, the overlap may extend over at least 10% of the circumference ofthe annular barrier, preferably at least 15% of the circumference, morepreferably at least 30%, and even more preferably at least 40% of thecircumference.

Moreover, the strands may abut each other.

In addition, the bundle and/or the strands may be coated with a secondmaterial selected from the group of metal, polymers, teflon and rubber,or a combination thereof.

Further, the strands may be twisted around each other, braided or mayform a yarn.

Also, the strands may enclose a core.

The present invention further relates to an annular barrier as describedabove, wherein the tubular part for mounting as part of the well tubularstructure has a longitudinal axis, and the expandable sleeve surroundingthe tubular part defines a space being in fluid communication with aninside of the tubular part, each end of the expandable sleeve beingconnected with the tubular part, wherein the annular barrier furthercomprises an aperture for letting fluid into the space to expand thesleeve.

In an embodiment, the expandable sleeve may be made of metal.

In another embodiment, the aperture may be arranged in the tubular part.

In yet another embodiment, the annular barrier may be a packer arrangedto seal against an inner surface of a well tubular structure.

The annular barrier as described above may further comprise an adhesivebetween the outer face and the annular seal.

The present invention further relates to a downhole annular sealcomprising:

-   -   a sealing material having at least one strand comprising        graphite and/or carbon.

Also, the present invention relates to a downhole system comprising awell tubular structure and at least one annular barrier as describedabove, wherein the annular barrier comprises a tubular structure mountedas part of the well tubular structure.

The downhole system as described above may further have a toolcomprising isolation means isolating an isolated part of the inside ofthe tubular part outside the aperture to pressurise the isolated part ofthe inside and the space to expand the expandable sleeve.

Said tool may further comprise a pumping device for pumping fluid fromthe inside of the tubular part being outside the isolated part and intothe isolated part to expand the expandable sleeve.

Additionally, the present invention relates to a manufacturing methodfor manufacturing a annular barrier as described above, comprising thesteps of:

-   -   winding the sealing material around the outer face of the        annular barrier to form the annular seal, and    -   fastening the sealing material by providing an adhesive between        the sealing material and outer face of the annular barrier.

The present invention further relates to an application method ofproviding an annular barrier in a casing or borehole, comprising thesteps of:

-   -   inserting an annular barrier in the casing or borehole having x        windings of sealing material around the outer face, where x>1.0,        and    -   expanding the annular barrier so that the annular barrier has y        windings of sealing material around the outer face, wherein y<x.

In an embodiment of the application method, x may be >1.5 and y may be>1.0.

When expanding the annular barrier, the winded sealing material unwindsitself, and as a result, the unwinded sealing material has y windings.

In another embodiment, the annular barrier may be expanded from a firstdiameter to a second diameter, the second diameter being larger than thefirst diameter.

Finally, the sealing material may have substantially the same lengthbefore and after expansion of the annular barrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its many advantages will be described in more detailbelow with reference to the accompanying schematic drawings, which forthe purpose of illustration show some non-limiting embodiments and inwhich

FIG. 1 shows an annular barrier according to the invention in itsunexpanded condition,

FIG. 2 shows the annular barrier of FIG. 1 in its expanded condition,

FIG. 3 shows another embodiment of the annular barrier,

FIG. 4 shows yet another embodiment of the annular barrier,

FIG. 5 shows en expanded view of part of FIG. 4 in which the annularbarrier is unexpanded,

FIG. 6 shows en expanded view of part of FIG. 4 in which the annularbarrier is expanded,

FIGS. 7 a-11 b show different embodiments of the annular seal seen in across-sectional view and in a side view, and

FIG. 12 shows a downhole system.

All the figures are highly schematic and not necessarily to scale, andthey show only those parts which are necessary in order to elucidate theinvention, other parts being omitted or merely suggested.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show an annular barrier 1 for providing zone isolationbetween a first zone 2 and a second zone 3 in a borehole 20. The annularbarrier 1 may also be set to provide zone isolation between a first zone2 and a second zone 3 in a casing downhole, e.g. when arranging aproduction casing within an intermediate casing. The annular barrier 1has an outer face 5 and a circumference varying from a first, unexpandeddiameter to a second, expanded diameter. The annular barrier comprisesseveral annular seals 4, each made of a sealing material 6 having abundle 7 of strands 8, wherein at least one strand comprises graphiteand/or carbon. Each strand comprises at least 30% graphite and/orcarbon, preferably at least 50% graphite and/or carbon, more preferablyat least 75% graphite and/or carbon, and even more preferably at least90% graphite and/or carbon. In this way, the seals of the annularbarrier can withstand very high temperatures, such as up to 650° C., anda high pressure, such as up to 450 bar, downhole. Seals of graphite orcarbon are also capable of withstanding hot steam or other gasses, lyesand acid, such as sulphur and nitride. Known elastomeric seals are notcapable of withstanding such harsh downhole conditions over a longerperiod of time, such as over a time span of 10 to 20 years, before theydisintegrate, dissolve or crack.

The annular barrier of FIG. 1 comprises a tubular part 9 for mounting aspart of the well tubular structure 10, the tubular part having alongitudinal axis 11 and being mounted as part of a well tubularstructure 10 for e.g. production casing. The annular barrier 1 has anexpandable element which in FIG. 1 is an expandable sleeve 12surrounding the tubular part and defining a space 13 being in fluidcommunication with an inside 14 of the tubular part. Each end 15, 16 ofthe expandable sleeve is connected with the tubular part in connectionparts 17, and the tubular part has an aperture 18 for letting fluid intothe space 13 to expand the sleeve. One end 15 is slidably connected withthe tubular part 9, and seals 19 are arranged in grooves 21 of theconnection part 17, and the other end 16 is fixedly connected with thetubular part 9. In the following, the annular barrier will be disclosedas an annular barrier having the expandable sleeve and the tubular justdescribed, but the annular barrier may also be a packer set arrangedbetween a first tubular 22 and second tubular 23, as shown in FIG. 3,where projections 24 press the annular seal 4 against an inner face 25of the second tubular 23.

As can be seen in FIG. 1, the sealing material of the annular sealextends around the outer face of the annular barrier for one annularseal 4. The annular seal has an elongated shape and two ends 27, 28, andthe ends overlap so that one end 27 is arranged opposite the other end28 of the annular seal 4. The sealing material is wound around the outerface of the annular barrier with x windings, where x>1.0. x is 1.0 ifthe ends 27, 28 face each other and x>1.0 if one end 27 is arrangedopposite the other end 28 of the annular seal 4 and lies in two layersat least partly around the outer face. In FIG. 1, the annular barrier isin its unexpanded position, and x is between 1.0 and 2.0, and maypreferably be between 1.1 and 1.7 and more preferably between 1.2 and1.5. When the annular barrier is in its unexpanded condition, theoverlap extends over at least 10% of the circumference of the annularbarrier, preferably at least 15% of the circumference, more preferablyat least 30%, and even more preferably at least 40% of thecircumference. The extent of the overlap depends on how much the outerdiameter of the annular barrier is to be increased during the expansion,and thus on the differences in the circumference before and afterexpansion.

When expanding the annular barrier 1, the sleeve 12 presses against theinner face 26 of the borehole 20, as shown in FIG. 2, thus pressing theannular seals against the inner face 26 and thereby squeezing theannular seals in between the sleeve and the inner face. As the sleeveexpands, the sealing material unwinds so that the ends 27, 28 (shown inFIG. 1) of the annular seal 4 no longer overlap, as shown in FIG. 2.

In order to hold the sealing material in place during insertion of theannular barrier down through the well, the annular barrier furthercomprises an adhesive between the outer face and the sealing material ofthe annular seal. The overlapping end arranged opposite the innermostend may also be adhered to the other end. After expansion, the annularseal no longer needs to be adhered to the outer face as it is squeezedin between the sleeve and the inner face 26. In FIGS. 1 and 2, thesealing material covers less than 40% of the outer face, and in FIG. 4,it covers preferably less than 30% of the outer face, and morepreferably less than 20% of the outer face.

In FIG. 4, the annular seals 4 are arranged in external safety sleeves37 fastened to the expandable sleeve 12 by a first connection 38 and asecond connection 39. In FIG. 4, the annular barrier is shown in itsexpanded condition, and FIG. 5 shows an enlarged view of one of theexternal safety sleeves 37 of the annular barrier, the annular barrierbeing in its unexpanded condition. Five annular seals are arranged onthe outer face of the annular barrier, i.e. on the outer face of theexternal safety sleeve 37. In the unexpanded condition of the annularbarrier, the ends 27, 28 of the annular seals 4 overlap, as shown inFIG. 5. The external sleeve has a trapezoidal cross-sectional shapeholding the annular seals 4 closely together. In FIG. 6, the annularbarrier has been expanded, and the annular seals 4 have been unwound,meaning that the ends of the annular seals no longer overlap. In FIG. 6,fluid from one isolation zone has entered an opening 30 in the externalsafety sleeve 37 and presses the annular seals even further against theinner face 26 of the borehole 20.

As can be seen in FIGS. 1-6, the cross-sectional shape of the annularseal is substantially square, but may, in another embodiment, haveanother shape, such as a triangular shape, a pentagonal shape, ahexagonal shape or a shape having more sides.

In FIGS. 7 a-11 b, the different embodiments of the annular seal areshown. In FIGS. 7 a, 8 a, 9 a, 10 a and 11 a, cross-sections of theannular seal are shown, and FIGS. 7 b, 8 b, 9 b, 10 b and 11 b show theannular seal from a side. In FIGS. 7 a and 7 b, the bundle 7 of strands8 is wound or braided together by means of another material 40 into ayarn in which the four strands lie straight along the longitudinalextension of the yarn so that they are substantially unbent. In FIG. 8a, braided strands 8 in a bundle 7 themselves form the yarn-like patternshown in FIGS. 8 a and 8 b. In FIGS. 9 a and 9 b, the bundled strands 8are wound or braided together by means of another material 40 into ayarn pattern 41, and the strands form a core 42. In FIGS. 10 a and 10 b,the bundled strands 8 are wound or braided around a core 42 of anothermaterial. In FIGS. 11 a and 11 b, the bundled strands 8 are twistedforming a coiling pattern 43, and the strands abut each other.

In FIGS. 7 a and 9 a, the other material 40 may be a material selectedfrom the group of metal, polymers, teflon and rubber, or a combinationthereof. The bundle of strands 8 may be coated with a second materialselected from the group of metal, polymers, teflon, an elastomericmaterial, silicone, natural or synthetic rubber or a combinationthereof. In this way, the sealing ability of the annular seal issubstantially increased.

FIG. 12 shows a downhole system 100 comprising a well tubular structure10 and two annular barriers having a tubular part 9 mounted as part ofthe well tubular structure 10. The downhole system 100 may further havea tool comprising an isolation means isolating an isolated part of theinside 14 of the tubular part opposite the aperture 18 to pressurise theisolated part of the inside 14 and the space 13 to expand the expandablesleeve. The tool may further comprise a pumping device for pumping fluidfrom the inside of the tubular part being outside the isolated part andinto the isolated part to expand the expandable sleeve.

When manufacturing an annular barrier 1, the expandable sleeve 12 isfastened in the connection parts 17, and the sealing material is woundaround the outer face of the annular barrier to form the annular seal.The sealing material is fastened to the outer face by providing anadhesive between the sealing material and the outer face of the annularbarrier. The annular barrier is then inserted into the casing orborehole having x windings of sealing material around the outer face,where x>1.0, and when the annular barrier is subsequently expanded, theannular barrier has y windings of sealing material around the outerface, wherein x>y. The sealing material extends around the outer face ofthe annular barrier so that the ends overlap when seen along in thelongitudinal extension of the tool. The number of windings x before theannular barrier is expanded is typically between 3 and 100, depending onthe length of the barrier. The number of windings y after expansion ofthe annular barrier is most often at least 1.0, preferably at least 1.5.

The sealing material of each annular seal has substantially the samelength before and after expansion of the annular barrier, and in thisway, the strands are not broken into several pieces, which would ruinthe sealing ability of the annular seal. Graphite and carbon are notvery bendable materials, but when they are wound, some kind offlexibility is built into the annular seal 4. When one end 27 of theannular seal overlaps the other end 28 and the expandable sleeve 12 isexpanded, the strands 8 may unwind themselves slightly so that thestrands of one end 27 lie between the strands of the other end 28 of theannular seal, and the annular seal in that section is thus wider thanannular seals in other sections.

An annular barrier may also be called a packer or a similar expandablemeans. The well tubular structure can be the production tubing or casingor a similar kind of tubing downhole in a well or a borehole. Theannular barrier can be used both in between the inner production tubingand an outer tubing in the borehole or between a tubing and the innerwall of the borehole. A well may have several kinds of tubing and theannular barrier of the present invention can be mounted for use in allof them.

A valve may be arranged in the aperture 18, and the valve may be anykind of valve capable of controlling flow, such as a ball valve,butterfly valve, choke valve, check valve or non-return valve, diaphragmvalve, expansion valve, gate valve, globe valve, knife valve, needlevalve, piston valve, pinch valve or plug valve. The aperture may bearranged opposite a connection part, and the connection part may have afluid channel fluidly connecting the aperture and the space 13.

The expandable sleeve may be an expandable tubular metal sleeve which isa cold-drawn or hot-drawn tubular structure.

When the expandable sleeve 12 of the annular barrier 1 is expanded, thediameter of the sleeve is expanded from its initial unexpanded diameterto a larger diameter. The expandable sleeve 12 has an outside diameterand is capable of expanding to an at least 10% larger diameter,preferably an at least 15% larger diameter, and more preferably an atleast 30% larger diameter than that of an unexpanded sleeve.

Furthermore, the expandable sleeve 12 has a wall thickness which isthinner than a length of the expandable sleeve, the thickness preferablybeing less than 25% of the length, more preferably less than 15% of thelength, and even more preferably less than 10% of the length.

The expandable sleeve 12 of the annular barrier 1 may be made of metal,polymers, an elastomeric material, silicone or natural or syntheticrubber.

In order to increase the thickness of the sleeve 12, an additionalmaterial may be applied (not shown) onto the expandable sleeve, e.g. byadding welded material onto the outer face.

In another embodiment, the thickness of the sleeve 12 may be increasedby fastening a ring-shaped part onto the sleeve (not shown).

In yet another embodiment, the increased thickness of the sleeve 12 maybe facilitated by using a varying thickness sleeve 12 (not shown). Toobtain a sleeve of varying thickness, techniques such as rolling,extrusion or die-casting may be used.

The fluid used for expanding the expandable sleeve may be any kind ofwell fluid present in the borehole surrounding the tool and/or the welltubular structure 3.

Also, the fluid may be cement, gas, water, polymers or a two-componentcompound, such as powder or particles mixing or reacting with a bindingor hardening agent. Part of the fluid, such as the hardening agent, maybe present in the cavity between the tubular part and the expandablesleeve before injecting a subsequent fluid into the cavity.

By fluid or well fluid is meant any kind of fluid that may be present inoil or gas wells downhole, such as natural gas, oil, oil mud, crude oil,water, etc. By gas is meant any kind of gas composition present in awell, completion, or open hole, and by oil is meant any kind of oilcomposition, such as crude oil, an oil-containing fluid, etc. Gas, oil,and water fluids may thus all comprise other elements or substances thangas, oil, and/or water, respectively.

By a casing is meant any kind of pipe, tubing, tubular, liner, stringetc. used downhole in relation to oil or natural gas production.

In the event that the tool is not submergible all the way into thecasing, a downhole tractor can be used to push the tool all the way intoposition in the well. The downhole tractor may have projectable armshaving wheels, wherein the wheels contact the inner surface of thecasing for propelling the tractor and the tool forward in the casing. Adownhole tractor is any kind of driving tool capable of pushing orpulling tools in a well downhole, such as a Well Tractor®.

Although the invention has been described in the above in connectionwith preferred embodiments of the invention, it will be evident for aperson skilled in the art that several modifications are conceivablewithout departing from the invention as defined by the following claims.

1-23. (canceled)
 24. An annular barrier for providing zone isolationbetween a first zone and a second zone in a borehole or a casingdownhole, the annular barrier comprising a tubular part and anexpandable element made of metal surrounding the tubular part, and theannular barrier having a circumference, a longitudinal extension and anouter face and further comprising an annular seal comprising a sealingmaterial, the sealing material extending around the outer face of theannular barrier and having a bundle of strands wherein at least onestrand comprises graphite and/or carbon.
 25. An annular barrieraccording to claim 24, wherein the strands comprise at least 30%graphite and/or carbon, preferably at least 50% graphite and/or carbon,more preferably at least 75% graphite and/or carbon, and even morepreferably at least 90% graphite and/or carbon.
 26. An annular barrieraccording to claim 24, wherein each strand comprises graphite and/orcarbon.
 27. An annular barrier according to claim 24, wherein thesealing material is wound around the outer face of the annular barrierwith x windings, where x>1.0.
 28. An annular barrier according to claim24, wherein the annular seal has an elongated shape and two ends.
 29. Anannular barrier according to claim 28, wherein the ends overlap whenseen in the longitudinal extension.
 30. An annular barrier according to28, wherein the annular seal is arranged side by side around the outerface as windings.
 31. An annular barrier according to claim 30, whereinthe overlap extends over at least 10% of the circumference of theannular barrier, preferably at least 15% of the circumference, morepreferably at least 30%, and even more preferably at least 40% of thecircumference.
 32. An annular barrier according to claim 24, wherein thesealing material may cover less than 60% of the outer face, preferablyless than 40% of the outer face, and more preferably less than 30% ofthe outer face.
 33. An annular barrier according to claim 24, wherein across-sectional shape of the annular seal may substantially be atriangle, a square, a pentagon, a hexagon or a shape having more sides.34. An annular barrier according to claim 24, wherein the strands abuteach other.
 35. An annular barrier according to 24, wherein the strandsare twisted around each other, braided or forms a yarn.
 36. An annularbarrier according to claim 24, wherein the tubular part for mounting aspart of the well tubular structure has a longitudinal axis, and theexpandable sleeve surrounding the tubular part defines a space being influid communication with an inside of the tubular part, each end of theexpandable sleeve being connected with the tubular part, wherein theannular barrier further comprises an aperture for letting fluid into thespace to expand the sleeve.
 37. An annular barrier according to claim24, wherein the aperture is arranged in the tubular part.
 38. An annularbarrier according to claim 24, further comprising an adhesive betweenthe outer face and the annular seal.
 39. A downhole system comprising awell tubular structure and at least one annular barrier according toclaim 24, wherein the annular barrier comprises a tubular structuremounted as part of the well tubular structure.
 40. A manufacturingmethod for manufacturing a annular barrier according to claim 24,comprising the steps of: winding the sealing material around the outerface of the annular barrier to form the annular seal, and fastening thesealing material by providing an adhesive between the sealing materialand outer face of the annular barrier.
 41. An application method ofproviding an annular barrier according to claim 24 in a casing orborehole, comprising the steps of: - inserting an annular barrier in thecasing or borehole having x windings of sealing material around theouter face, where x>1.0, and - expanding the annular barrier so that theannular barrier has y windings of sealing material around the outerface, wherein y<x.
 42. An application method according to claim 41,wherein x>1.5 and y>1.0.
 43. An application method according to claim41, wherein the sealing material has substantially the same lengthbefore and after expansion of the annular barrier.